Chilled cast-iron roll



Patented eb. 12, -1929.

UNITED STATES CHARLES I. NIEDRINGHAUS AND LEWIS W. MESTA, F PITTSBURGH,PENNSYLVANIA,

ASSIGNORS TO MESTA. MACHINE COMPANY, OF PITTSBURGH, PENNSYLVANIA, A.

CORIOBATION OF PENNSYLVANIA.

GHILLED CAST-IRON ROLL.

Ho Drawing.

us and low sulphur. We have found that by the use of relatively highchromium within the limits hereinafter specified and low phosphorus andlow sulphur, together with suit;

able control of the carbon and silicon, a chilled cast iron rolling millroll may be produced having both extraordinary hardness andextraordinary strength and toughness.

The roll is a cast iron roll, as distinguished from'a steel roll or a socalled Adamite roll. The melt should be made up m a furnace in which thecontrol of the low phosphorus and sulphur can be attained, such, forexample, as an air furnace, an open-hearth furnace or an electricfurnace. The charge may be made up in the usual way of pig iron, scrapand ferrochromium additions. The metal is cast in chill molds of theusual character. Such molds may consist of a heavy chill around theentire body of the roll or may consist of bands which chill certainportions of the body. The chillingbands may be heavy or light, as is thepractice in making the heavily chilled rolls or the lighter chilledrolls,-sometimes called condensed grain rolls.

The carbon of the roll is within the ranges of carbon for cast ironrolls. The carbon may vary from about 2.25% to about 3.75% or even asmuch as from about 2% to 4%. The chromium is much higher than has beenusually employed in making chilled cast iron rolls. The chromium mayvary from about 2% to 3%, .or even from 1.80% to 4%, although. we preferto have the chromium somewhere about 2.25% to 2.75%. The phosphorus iske t low. ,The. phosphorus should not exceed a out .30%, preferably notover about 2%. or .15%,;and for best results not over .10%. The sulphurshould also be kept low, not over about 20% preferably not over (if forthe bestresults about 15% or .10%, an not over ahout .08%. The manganesemay Wary within the usual ranges, say from about .1 to 1.50%, preferablyfrom about 15% to about .7 5% or 1%. The silicon will be varied inaccordance with the carbon and chromium and the size of the roll. Thesilicon will ordinarily be within the ranges from about .50% to 2.25% or2.50%, preferably over 1%. The silicon will ordinarily be Applicationfiled May 19,

1927. serial No. 192,783.

higher than that of the usual chilled iron rolls. The control of thesilicon, together wlth the chromium and carbon, is important in givingthe extraordinary'toughness to the .roll. It IS preferred to use enoughsilicon so that there will be a very slight precipitation of graphitethrough the chill portion of the roll. By this, we do not mean that thechill portion of the roll will be of a gray or mottled iron. The chillportion of the roll is predominately a white iron, but is characterizedby microscopic flecks of graphitic carbon throughout its greater part.Under some conditions, there may be a relatively thin zone or skin ofpure white metal at the free surface of the roll, but the greater partof the chill portion of the roll preferably exhibits the fine, graphiticcarbon. I

The tendency of the high carbon is, of course, to precipitate asgraphite. This tendency is, however, restrained by the relatively highchromium content. The chromium tends to hold the carbon in the combinedform, and when chilled, to produce a white iron which, althou h it tendsto be hard, is inclined to be rittle. We have found that if the actionof the carbon and chromium is suitably controlled by the sili con to apoint where a very small but appreciable amount of graphitic carbon isprecipitated, the roll will be much stronger than an ordinary. chillediron roll and will also have a greater hardness due to its high chromiumand carbon. The amount of silicon and cartendency of the chromium tomake the hot metal mushy and assists in the control and pouring of aheat of the metal.

Thereis a greater tendency toward white iron in the interior of the rollthan with the usual chilled iron roll, due to the high chro- This isapparently the cause of the gradual and imperceptible shading oif of themetal structure from the exterior toward the interior of the roll. Atthe surface of the roll where the metal is more heavily chilled, themetal will be predominantly a white iron which preferably contains asmall but still microscopically distinguishable amount of finelydistributed graphitic carbon. In going from the surface of the rolltoward the interior, there is no abrupt change in the grain structure ofthe meta or in the amount of graphitic carbon, as is the case in theordinary chilled roll, where there is a fairly distinct line ofdemarkation between the chilled portion and the underlying core ofmottled iron.

'lhegraphite in the chilled portion exists in a very finely dividedform. The granules by the eye.

ward white iron than that of the core of the usual chilled iron'roll.The roll, therefore, appears to have a relatively deep chill whichgradually tapers OK or disappears toward the interior of the roll. Thisadapts the roll particularly for work in which.

grooves are to be cut into the roll. Also it permits the rolls to beturned down considerably before their usefulness is destroyed.

While ordinarily the presence of a small but appreciable amount offinely divided graphitic carbon Will persist to the very exterior of theroll, under some circumstances, the exterior or skin of the roll may beof a practically pure white iron, particularly in; the case of heavychilling and toward the lower ranges'of the silicon and carbon and Yupper ranges of the chromium. lVhen such white iron skin or zone occurs,it merges grad ually and imperceptibly into the underlying metal inwhich the finely divided graphitic carbon is present. Y

The chill portion of our roll is character ized, as contrasted with theordinary chill, by the presence of the small but appreciable amounts ofvery finely divided graphitic carbon and by its gradual andimperceptible merger with the metal at the interior of the roll. lfhe'chill, while containing "a small amount of graphitie carbon, isnevertheless hard as, and usually harder than, the ordinary white ironchills; We believe that the extraordinaryhardness of the chill is due tothe combination of the chromium with the carbon and that theextraordinary strength in the presence of the high chromium is due tothe condition of the iron. brought about by the control of the chromium,carbon and silicon, in which the small amount of microscopicallydistributed graphitic carbon is present,

The chromium is one of the cheapest alloying metals and we are enabledto get the combined strength and hardness by the use of chromium alone,and without the more expensive alloying metals which have been suggestedfor use in chilled cast iron rolls. However, small amounts of otheralloying elements may be present, if desired, such for example, as smallamounts of nickel, cobalt, uranium, vanadium, molybdenum, tungsten, etc.1

While we have described the preferred embodiment of our invention, bothas to its preferred analyses and preferred physical characteristics, itis to be understood that the invention is not so limited, but may beotherwise embodied within the scope of the following claims.

We claim: 1. A chilled cast iron roll containing carbon about 2% to 4%,chromium about 1.80% to 4%, phosphorus not over about 30%, sulphur notover about .20%, manganese about 110% to 1.50%, and silicon about 50% to2.50%,the silicon, carbon and chromium being so proportioned as toproduce a chill containing a small but appreciable amount of very finelydivided graphitic carbon and the said chill merging gradually andwithout abrupt change of grain structure into a core of mottled ironwhich has a greater tendency.

toward white iron than that. of the usual chilled iron roll.

.2. A chilled castiron roll containing carbon about 2% to l%, chromiumabout 2% to 4%, phosphorus not over about 30%, sulphur not over about10%, manganese about .10%

to 1.50%, and silicon about 1% to 2.50%, the

silicon, carbon and chromium being so proportioned as toproduce a chillcontaining a small but appreciable amount of very finelydivided'gzraphitic carbon and the said chill merging gradually andwithout abrupt change of grain structure into a core of mottled ironwhich has a greater tendencytoward white iron than that of the usualchilled iron roll.

In testimony whereof we have-hereunto set our hands.

crrannns i. nrnnninenans. LEWIS w. MESTA. i

